1. Field of the Invention
This invention relates to improvements in heat treating pulverous raw material such as cement raw meal, lime, aluminum oxide and the like.
2. Description of the Prior Art
In the technology pertaining to the heat treatment of pulverous raw material it is often desirable, if not necessary, to divide a flow of the hot pulverous material into two or more parallel, equal material sub-flows. Thus it may be necessary to subject the pulverous material to two successive heat treatments of a different nature. For example, the material may be subjected to a preheating treatment which is succeeded by a calcining, of which at least the first heat treatment takes place by heat exchange with a hot gas in which the pulverous material is suspended. Further, it may be advantageous to carry out the preheating in one suspension heat exchanger and to effect the subsequent calcination in two or more heat treatment units (calciners) working in parallel. It is therefore of great significance to separate the flow of hot pulverous material after being subjected to the initial heat treatment in the suspension such that it can be passed to the succeeding two or three heat treatment units in separate flows which are of substantially equal volume and temperature.
One technique which has been employed to divide the flow of material into at least two equal sub-flows has been to insert an adjustable flap damper of known construction into the discharge pipe of the suspension heat exchanger and to divide the pipe into two parallel pipes beneath the flap damper. By proper adjustment of this damper -- and by re-adjustment -- e.g. automatically -- from time to time it should be possible always to ensure two identical flows of material through the two discharge pipes beneath the damper. However, this has proven to be a solution that is not satisfactory under actual working conditions. For example it is unreliable and complicated. Further, it requires constant -- e.g. automatic -- attention, and is hardly practical if division into three or maybe four flows is demanded.
It should also be noted that the chief objection to the use of a steel flap damper is that the temperature of the pulverous material to be divided is often very high, of the order 800.degree.-900.degree. C., and these temperatures have been found to be so high that an ordinary flap damper of steel construction would soon be destroyed.
The temperature in the lowermost part of the suspension heat exchanger, which is made of steel, is also very high, but the exposed parts -- which include internal and external connecting pipes -- are always provided with a refractory lining, and are consequently not damaged. It has been determined that even though the damper and the casing in which it is placed were made of fire-resistant, alloy steel, the durability thereof would be extremely restricted. For example, if these parts were made of ceramic fire-resistant material or clad with such a material, the damper structure would be heavy and clumsy, and it would be impossible to make it gas-proof. Similar objections have been advanced with respect to a hollow water cooled damper placed in a casing with hollow, water-cooled walls.
It is therefore clear that the use of a flap damper does not provide a satisfactory solution of the problem. Moreover, up to the present, no known satisfactory solution to this problem has yet been advanced.
U.S. Pat. No. 3,881,861 to Ritzmann (which corresponds to German Pat. No. 2.247.172) relates to an Apparatus For The Manufacturing Of Cement. Cement raw material exiting the penultimate stage of a preheater is divided into two streams by subjecting the flow to a counterflow of gas and by permitting the entrained raw material to pass into either of two sub-pipes which branch from the main riser pipe. The material flows into final preheater sections and into an idling chamber wherein the preheated raw material is kept circulating in a stream of hot gas for a predetermined time before entering a rotary tube furnace via a flap damper of the type heretofore described. U.S. Pat. No. 3,317,201 to Heins-Gert Muller et al relates to a Method Of And Arrangement For Increasing The Alkali Content In Alakli Laden Dusts Of Flue Gases. Cement raw material is passed through successive stages of a preheater countercurrent to a flow of hot gas. In the upper stages of the preheater the material flowing from one stage is divided into two unregulated flows and reunited in the succeeding stage and this process ceases at the penultimate stage. I have devised a method and apparatus which are particularly suitable for incorporation as part of a rotary kiln plant which readily and efficiently achieves the desirable separate division flows of material while substantially avoiding the disadvantages of the prior art.